Producing alkylate of reduced copper corrosivity



tinned Statm Patent 9 3,014,794 PRODUCING ALKYLATE F REDUCED COPPER CORROSIVITY Norman R. Le Roy, Manhattan Beach, Calif., assignor to California Research Corporation, San Francisco, Calif.,

a corporation of Delaware No Drawing. Filed Feb. 9, 1960, Ser. No. 7,526 4 Claims. (Cl. 44-76) This invention relates to improvements in the art of alkylating olefins with isoparaflins in the presence of a sulfuric acid catalyst. h particular, the invention is concerned with a method of reducing the copper strip corrosivity of alkylate produced by the sulfuric acid process.

Alkylation is widely practiced as a method of producing gasolineboiling range hydrocarbons from lower molecular weight hydrocarbons. In the sulfuric acid alkylation process an isoparafiin, such as iso butane, is condensed with a mono-olefin, such as butylene, in the liquid phase at temperatures of 0-100" 'F. and in the presence of sulfuric acid. The hydrocarbon phase, or whole alkylate, is separated from the acid, neutralized with caustic, water washed, and distilled to separate unreacted light hydro carbons and heavy alkylate from the gasoline boiling range product alkylate. The alkylate so produced by condensing isobutane with butylene is particularly well suited for use as aviation gasoline or as a major constituent in blended aviation gasoline. Generally, the gasoline may comprise from 25% to 75% alkylate, by volume, depending on the grade of gasoline.

Aviation gasoline specifications as set out in ASTM D-9l0 require that the gasoline pass the copper strip corrosion test, as described in ASTM D-l30-56. As appli d to gasoline, the copper strip corrosion test involves immersing a polished copper strip in a given quantity of the gasoline and then heating the stock for two hours at 212 F. in a closed container. The copper strip is then removed, washed, and rated by comparing visually with the ASTM copper strip corrosion standards. As applied to aviation gasoline, the test is reported as passing it there is no more than slight discoloration (strip numbers 0, 1A, or 1B). The copper strip test is indicative of the corrosivity of the stock, and it is highly sensitive in the detection of minute quantities of corrosive impurities.

Where the aviation gasoline contains alkylate produced by the sulfuric acid process, difliculty is sometimes encountered in passing this test. This problem periodically arises even though there has been no immediately apparent change in the alkylation operating conditions or in the neutralization, water-washing, or distillation steps.

It is an object of this invention to produce an alkylate which does not appreciably discolor a copper strip immersed therein for two hours at 212 F. A further object of the invention is to provide a method of reducing the copper strip corrosivity of the alkylate.

I have discovered that the copper strip corrosivity of alkylate produced by the sulfuric acid process can be reduced or, in most instances, completely eliminated by adding to the alkylate a minute quantity of a lower alkyl mercaptan. Briefly, the invention comprises adding to the allcylate a minor amount of alkyl mercaptans having less than six carbon atoms to the molecule, to provide a mercaptan concentration in the alkylate of from about 0.1 p.p.m. to less than 3 p.p.m. by volume, suflicient to inhibit the copper strip discoloration. Generally, less than 2 p.p.m. of mercaptan is required. At the low concentrations used the quantity of mercaptan is not sufiicient to impart a disagreeable odor or to affect adversely any of the other specifications of the alkylate or gasoline containing the alkylate. The mercaptan concentration should be held below about 4 p.p.m. if the stock is required to 3,014,794 Patented Dec. 26, 1961 pass the doctor test, which is commonly required of military aviation gasoline although not specified in ASTM D-910. Additionally, with mercaptan concentrations above 3 p.p.m., there is a tendency to form white deposits in the copper strip test.

The meroaptans which may be used in the method of this invention comprise lower alkyl merc-aptans, having less than 6 carbon atoms to the molecule, i.e., methyl, ethyl, propyl, butyl, and amyl mercaptans. P-ropyl, butyl, and amyl mercaptans are preferred because of their favorable boiling points. Mixed mercaptans containing one to five carbon atoms to the molecule have also been employed to advantage. The mercaptans are added to the finished alkylate obtained by caustic washing the crude whole alkylate, water washing, and distilling. A typical process flow and distillation scheme is described in US.

Patent No. 2,346,770 to P. Lobdell and G; L. Mateer. Obviously, the mercaptans could be added later after blending of the alkylate with other gasoline stocks to form the finished gasoline. However, it is preferred that all blending stocks be brought on specification prior to blending.

Example I Butyl Mercaptan Concentration Untreated Alkylate 0.5 1 2 p.p.m. p.p.m. p.p.m.

Copper Strip Rating 2A 1A 1A 1A In the evaluation of the copper strip test results, a rating of 2A indicates modenate tarnishing, in this case a claret red appearance. A rating of 1A indicates a light orange color, almost the same as a freshly polished strip.

Example H Finished alkylate, recovered from whole alkylate as in Example I, had a copper strip rating of 2B (lavender). Treatment with butyl mercaptan brought the alkylate on specification, as shown by the data presented in the following t'a'ble:

Butyl Mercaptan Concenation Untreated Alkylate 1 2 3 p.p.m. p.p.m. p.p.m.

Copper Strip Ratlng 2B 1B 1A 1A (White powder than).

Example 111 I Another sample of finished alkylate, recovered from whole alkylate in the same manner as in Example I, had

a copper strip rating of 2A. After the addition of 1 p.p.m.

by volume of isopropyl mercaptan the copper strip rating was 1A.

Example IV One part per million by volume of mixed mercaptans, comprising C -C mercaptans, was added to causticwashed water-washed, and distilled finished alkylate having a copper strip test rating of 2A. The treated alkylate had a copper strip rating of 1A. The treated alkylate was blended with an aromatic distillate, primarily toluene, to produce an aviation gasoline containing 75 percent by volume treated alkylate, which gasoline was doctor sweet and passed all specifications set out in ASTM D-910.

The addition of lower alkyl mercaptans is also effective in improving the copper strip test of alkylate initially having a copper strip test of 3 (brassy tarnish) or 4 (black). However, a test of 4 indicates such severe contamination of the alkylate that it should instead be redistilled or otherwise purified, as by further caustic and water washmg.

What I claim is:

l. The method of producing alkylate of reduced copper corrosivity, said alkylate being prepared by reacting an olefin with an isoparaffin in the presence of a sulfuric acid catalyst, which comprises neutralizing and water-Washing alkylate separated from the reaction mixture and then treating the alkylate with a minor amount of a lower alkyl mercaptan to provide a mercapt-an concentration in the alkylate of from about 0.1 ppm. to less than 3 ppm. by volume.

2. The method of claim 1 wherein the mercaptan added is butyl mercaptan.

3. The method of claim 1 wherein the mercaptan added is a mixture of C -C mercaptans.

4. An aviation gasoline comprising predominantly alkylate, which gasoline does not discolor a copper strip immersed therein for two hours at 212 F., prepared by adding -a minor amount, in the range 0.1 to less than 3 p.p.m. by volume, of alkyl mercaptans having less than 6 carbon atoms to the molecule to a neutralized waterwashed and distilled finished alkylate, produced by condensing isobutane with butylene in the presene of a sulfuric acid catalyst, and blending the alkylate with a gasoline boiling range distillate.

References Cited in the file of this patent UNITED STATES PATENTS 2,033,377 Burk Mar. 10, 1936 2,222,122 Schulze et al Nov. 19, 1940 2,880,255 Davis et a1. r s Mar. 31, 1959 

4. AN AVIATION GASOLINE COMPRISING PREDOMINANTLY ALKYLATE, WHICH GASOLINE DOES NOT DISCOLOR A COPPER STRIP IMMERSED THEREIN FOR TWO HOURS AT 212*F., PREPARED BY ADDING A MINOR AMOUNT, IN THE RANGE 0.1 TO LESS THAN 3 P.P.M. BY VOLUME, OF ALKYL MERCAPTANS HAVING LESS THAN 6 CARBON ATOMS TO THE MOLECULE TO A NEUTRALIZED WATERWASHED AND DISTILLED FINISHED ALKYLATE, PRODUCED BY CONDENSING ISOBUTANE WITH BUTYLENE IN THE PRESENCE OF A SULFURIC ACID CATALYST, AND BLENDING THE ALKYLATE WITH A GASOLINE BOILING RANGE DISTILLATE. 